This is the 853rd most frequent Serbian word.
заинтересовани
Interested.
Here, 'заинтересовани' is used as an adjective to describe the subject 'we' being interested in something.
Ми смо заинтересовани за ваш предлог.
We are interested in your proposal.
The word 'заинтересовани' here explains the state of being interested, attributed descriptively to 'they'.
Њихова реакција показује да су заинтересовани.
Their reaction shows that they are interested.
In this question, 'заинтересовани' is used to inquire about someone's interest in a course, functioning as a predicate adjective.